• Air-cooled Engine for Double-decker
Page 40
Page 41
If you've noticed an error in this article please click here to report it so we can fix it.
• AFTER announcing last week that
the Birmingham and Midland Motor Omnibus Co., Ltd., had produced an• experimental air-cooled engine, Mr. D. M. Sinclair, general manager, stated that its performance 'characteristics were nearly comparable to those of its water-cooled counterpart and expressed his confidence in the engine as a suitable unit for a new double-decker being developed by the company. Mr. Sinclair hopes that the output of the engine will eventually surpass the performance of the watercooled type.
The crankcase assembly and pistons of the engine are identical to the parts of the company's 8-litre six-cylindered engine which develops 105 b.h.p. at 1,700 r.p.m. and a maximum torque
of350 lb. ft. at 1,100 r.p.m. The cylinder block is of cast-iron monobloc construction and is fitted with two heads. It is probable that light-alloy block and heads will later be developed, and this should reduce the overall weight of the unit to well below that of the standard 8-litre engine, as well as improving heat dissipation. The use of light allay would also facilitate casting. Fan Cooling _ In its existing experimental form. cooling is provided by asix-bladed light-alloy fan driven by an electric motor, mounted at the side of the test bed, and by two air' pumps which separately provide a draught of air to three injectors. The injectors are the only parts of the engine that have tended to overheat, but it is not considered that this represents a problem of any magnitude. Full details of the design plans for the production engine with regard to the cooling system are not available, but•a system will probably be developed in which air is drawn
r:6
past the engine bs., two rear-mounted fans, with a thermostatically controlled drive.
The form of the drive will be of the positive type to obviate danger of failure, and output wilt be closely controlled according to the temperature of the hottest parts of the head. The power consumption of the fans should not exceed about 4 b.h.p.
Separate porting is a feature of the inlet-valve layout, both the inlet and exhaust ports being arranged on the near side of the engine. Later units will be fitted with cylinder heads with inlet ports on the oilside, opposite tO
the exhaust ports. This should improve 'cooling. Ample air space between the cylinders is provided by the monobloc casting, and the dufting is shaped to direct-the air both longitudinally over the horizontal fins and transversely through the ait gaps, a relatively large air space on the off side promoting even distribution.
Flat deflector plates are fitted on the near side and at the rear. The system substantially increases the overall width of the engine, but the modified system will he much more compact. Apart from increasing the piston clearances_ and using hardened and tempered rings in place of the ehromium-plated type, no modifications have been made to the moving parts of the engine, and the shape of the combustion chamber is unchanged. It is possible, however, that the size of the exhaust valves will later be increased.
An S.A.E. 30 heavy-duty, lubricating oil is employed, water-cooled engines being normally run on an S.A.E. 10 oil. Fuel consumption on the test bed approximates to that of the conventional units, but an improvement in service is regarded as a hopeful possibility because of more rapid warming up.
Temperature Checks
Details of developtnent work include the use of temperature paints to check the maximum temperatures of the hottest parts of the head, and an interesting minor modification is the reduction of-the injector-body diameter above the flange to improve cooling.'
After witnessing a demonstration of the unit, a representative of The Commercial Motor reported that the noise level appeared to be normal, with the qualification that the engine produced a distinctive, but not offensive, highpitched ring. Techniciansof the company state that the unit runs more euietly than was expected and attribute this favourable characteristic, in part, to the form of ducting employed: Experiments may later be made with acoustic material further to reduce noise
The lack of cooling water for interior heating does not, it is considered, represent a difficult problem, despite the disadvantage with regard to fumes if the cooling air were ducted-tothe interior. An air-to-air heat exchanger could. it believed, • be successfully developed. possibly in conjunction with an exhaust. heated unit.
In conformity with the company's policy of standardizing 103-litre engines for double-deckers, an air-cooled unit.of this capacity will be developed in due course. Building a vertical engine before a horizontal type is an example of tackling the most difficult job first." The greater space available in the case of an underfloor-engined vehicle will obviate many problems.
A longer working life and reduced maintenance are the main benefits which air cooling is expected to provide, these gains being associated with the substantial reduction in running at sub-normal temperatures. This may also increase the mileages covered between oil changes by virtue of a relative freedom frorri oil contamination by acidic products of combustion.
If the air-cooled engine is produced in fairly large batches of around 250 units, it should be possible to build it at a cost comparable with that of the watercooled engine.
positions by a C-spring, and can be locked when closed, Recessed into the boot, the rear number plate is illuminated through a Perspex window from a light atting attached to the crib rail.
An example of the recent increase in the number of plastics bodywork components employed by the company is represented by the entrance doors, which comprise male and female mouldings bonded together with a steel stiffener, the steel member also acting as a tapping plate for the rubber damping pads. The doors are some 30 lb. lighter than metal doors, and it is anticipated that their low weight will reduce operating-gear maintenance. An interesting feature of the glasspol step is the use of tread plates which are impregnated with cast-iron filings.